Tympanic membrane repair using silk fibroin and acellular collagen scaffolds

Collagen Matrix to Restore the Tympanic Membrane: Developing a Novel Platform to Treat Perforations

Modern otology faces challenges in treating tympanic membrane (TM) perforations. Instead of surgical intervention, alternative treatments using biomaterials are emerging. Recently, we developed a robust collagen membrane using semipermeable barrier-assisted electrophoretic deposition (SBA-EPD). In this study, a collagen graft shaped like a sponge through SBA-EPD was used to treat acute and chronic TM perforations in a chinchilla model. A total of 24 ears from 12 adult male chinchillas were used in the study. They were organized into four groups. The first two groups had acute TM perforations and the last two had chronic TM perforations. We used the first and third groups as controls, meaning they did not receive the implant treatment. The second and fourth groups, however, were treated with the collagen graft implant. Otoscopic assessments were conducted on days 14 and 35, with histological evaluations and TM vibrational studies performed on day 35. The groups treated with the collagen graft showed fewer inflammatory changes, improved structural recovery, and nearly normal TM vibrational properties compared to the controls. The porous collagen scaffold successfully enhanced TM regeneration, showing high biocompatibility and biodegradation potential. These findings could pave the way for clinical trials and present a new approach for treating TM perforations.

Multimodal additive manufacturing of biomimetic tympanic membrane replacements with near tissue-like acousto-mechanical and biological properties

The three additive manufacturing techniques fused deposition modeling, gel plotting and melt electrowriting were combined to develop a mimicry of the tympanic membrane (TM) to tackle large TM perforations caused by chronic otitis media. The mimicry of the collagen fiber orientation of the TM was accompanied by a study of multiple funnel-shaped mimics of the TM morphology, resulting in mechanical and acoustic properties similar to those of the eardrum. For the different 3D printing techniques used, the process parameters were optimized to allow reasonable microfiber arrangements within the melt electrowriting setup. Interestingly, the fiber pattern was less important for the acousto-mechanical properties than the overall morphology. Furthermore, the behavior of keratinocytes and fibroblasts is crucial for the repair of the TM, and an in vitro study showed a high biocompatibility of both primary cell types while mimicking the respective cell layers of the TM. A simulation of the in vivo ingrowth of both cell types resulted in a cell growth orientation similar to the original collagen fiber orientation of the TM. Overall, the combined approach showed all the necessary parameters to support the growth of a neo-epithelial layer with a similar structure and morphology to the original membrane. It therefore offers a suitable alternative to autologous materials for the treatment of chronic otitis media. STATEMENT OF SIGNIFICANCE: Millions of people worldwide suffer from chronic middle ear infections. Although the tympanic membrane (TM) can be reconstructed with autologous materials, the grafts used for this purpose require extensive manual preparation during surgery. This affects not only the hearing ability but also the stability of the reconstructed TM, especially in the case of full TM reconstruction. The synthetic alternative presented here mimicked not only the fibrous structure of the TM but also its morphology, resulting in similar acousto-mechanical properties. Furthermore, its high biocompatibility supported the migration of keratinocytes and fibroblasts to form a neo-epithelial layer. Overall, this completely new TM replacement was achieved by combining three different additive manufacturing processes.

Application of Silk-Fibroin-Based Hydrogels in Tissue Engineering

Silk fibroin (SF) is an excellent protein-based biomaterial produced by the degumming and purification of silk from cocoons of the Bombyx mori through alkali or enzymatic treatments. SF exhibits excellent biological properties, such as mechanical properties, biocompatibility, biodegradability, bioabsorbability, low immunogenicity, and tunability, making it a versatile material widely applied in biological fields, particularly in tissue engineering. In tissue engineering, SF is often fabricated into hydrogel form, with the advantages of added materials. SF hydrogels have mostly been studied for their use in tissue regeneration by enhancing cell activity at the tissue defect site or counteracting tissue-damage-related factors. This review focuses on SF hydrogels, firstly summarizing the fabrication and properties of SF and SF hydrogels and then detailing the regenerative effects of SF hydrogels as scaffolds in cartilage, bone, skin, cornea, teeth, and eardrum in recent years.

Decellularized tympanic membrane scaffold with bone marrow mesenchymal stem cells for repairing tympanic membrane perforation

BACKGROUND

Tympanic membrane perforation (TMP) is a common disease in otology, and few acellular techniques have been reported for repairing this condition. Decellularized extracellular matrix (ECM) scaffolds have been used in organ reconstruction.

OBJECTIVE

This study on tissue engineering aimed to develop a tympanic membrane (TM) scaffold prepared using detergent immersion and bone marrow mesenchymal stem cells (BMSCs) as repair materials to reconstruct the TM.

RESULTS

General structure was observed that the decellularized TM scaffold with BMSCs retained the original intact anatomical ECM structure, with no cell residue, as observed using scanning electron microscopy (SEM), and exhibited low immunogenicity. Therefore, we seeded the decellularized TM scaffold with BMSCs for recellularization. Histology and eosin staining, SEM and immunofluorescence in vivo showed that the recellularized TM patch had a natural ultrastructure and was suitable for the migration and proliferation of BMSCs. The auditory brainstem response (ABR) evaluated after recellularized TM patch repair was slightly higher than that of the normal TM, but the difference was not significant.

CONCLUSION

The synthetic ECM scaffold provides temporary physical support for the three-dimensional growth of cells during the tissue developmental stage. The scaffold stimulates cells to secrete their own ECM required for tissue regeneration. The recellularized TM patch shows potential as a natural, ultrastructure biological material for TM reconstruction.

Histopathological Evaluation of Platelet-Rich Plasma Effect in Acute Tympanic Membrane Perforation

Platelet-rich plasma (PRP) is a reliable and has low side-effect profile and has beneficial effects on wound healing. Its investigatory effects on wound-healing process were shown on various tissues. This study aims to investigate PRP's local application effects to perforated rat TM in terms of healing and histopatological outcomes. Twenty-two Wistar rats were used in the study. The rats' ears were examined with a pediatric endoscope (2.7 mm, 0°), and the TM posterior quadrant of their right ear was perforated with a 20-gauge needle. After this procedure, the rats were divided into two equal groups. A spongel with PRP was applied on the perforated TM in the first group, and spongel with standard saline solution was applied on the second group. Following the sacrifice, the middle air bullas were carefully dissected and removed for histopathological examination. Hematoxylin eosin (for fibroblasts, lymphocyte, collagen fibers) and immunohistochemical staining were done for epithelial growth factor receptor (EGFR), fibroblast growth factor receptor (FGFR1), and vascular endothelial growth factor (VEGF) staining for histopathologic examinations. There was not a significant difference between the two groups for lymphocyte. There was a significant difference between control and study groups for collagen and EGFR (P < 0.05). Although the mean value of FGF- and VEGF-positive cells was higher in the study group than in the control group, the difference was not significant (P > 0.05). PRP is an effective autologous material for the healing process of acute TM perforations in a rat model, as demonstrated in the present study. We think that the use of PRP for acute TM perforations can have a positive effect on the healing process by increasing the level of growth factors, especially EGFR. In addition, an increase in collagen can also have a positive effect on healing.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-021-02912-2.

3D printing technology and applied materials in eardrum regeneration

Tympanic membrane perforation is a common condition in clinical otolaryngology. Although some eardrum patients can self-heal, a long period of non-healing perforation leads to persistent otitis media, conductive deafness, and poor quality of life. Tympanic membrane repair with autologous materials requires a second incision, and the sampling site may get infected. It is challenging to repair tympanic membranes while maintaining high functionality, safety, affordability, and aesthetics. 3D bioprinting can be used to fabricate tissue patches with materials, factors, and cells in a design manner. This paper reviews 3D printing technology that is being used widely in recent years to construct eardrum stents and the utilized applied materials for tympanic membrane repair. The paper begins with an introduction of the physiological structure of the tympanic membrane, briefly reviews the current clinical method thereafter, highlights the recent 3D printing-related strategies in tympanic membrane repair, describes the materials and cells that might play an important role in 3D printing, and finally provides a perspective of this field.

Tissue engineering and regenerative medicine strategies for the repair of tympanic membrane perforations

Despite the high success rate of autologous grafts in tympanic membrane repair, clinical alternatives are required for the closure of unresponsive chronic perforations that can lead to recurring infection and hearing loss. Tissue engineering and regenerative medicine approaches have emerged as another strategy to repair the eardrum, in addition to negating the need for donor tissue harvest and related surgical iatrogenicities. This review highlights the main approaches using biomaterials, growth factors, and cell therapies towards the healing of complex TM perforations. In addition, we discuss the challenges and advances for the development of reliable animal models, which will allow the optimisation and development of novel techniques. Finally, we indicate technologies that are currently used clinically and others that are closer to the market. The advances here discussed on tissue engineering and regenerative medicine strategies applied to the field of TM perforations will allow otologists, surgeons, and researchers to better bring novel technologies to the bedside as well as to develop new ones.

The possible mechanism of Hippophae fructus oil applied in tympanic membrane repair identified based on network pharmacology and molecular docking

OBJECTIVE

This study aimed to explore the mechanisms of Hippophae fructus oil (HFO) in the treatment of tympanic membrane (TM) perforation through network pharmacology-based identification.

METHODS

The compounds and related targets of HFO were extracted from the TCMSP database, and disease information was obtained from the OMIM, GeneCards, PharmGkb, TTD, and DrugBank databases. A Venn diagram was generated to show the common targets of HFO and TM, and GO and KEGG analyses were performed to explore the potential biological processes and signaling pathways. The PPI network and core gene subnetwork were constructed using the STRING database and Cytoscape software. A molecular docking analysis was also conducted to simulate the combination of compounds and gene proteins.

RESULTS

A total of 33 compounds and their related targets were obtained from the TCMSP database. After screening the 393 TM-related targets, 21 compounds and 22 gene proteins were selected to establish the network diagram. GO and KEGG enrichment analyses revealed that HFO may promote TM healing by influencing cellular oxidative stress and related signaling pathways. A critical subnetwork was obtained by analyzing the PPI network with nine core genes: CASP3, MMP2, IL1B, TP53, EGFR, CXCL8, ESR1, PTGS2, and IL6. In addition, a molecular docking analysis revealed that quercetin strongly binds the core proteins.

CONCLUSION

According to the analysis, HFO can be utilized to repair perforations by influencing cellular oxidative stress. Quercetin is one of the active compounds that potentially plays an important role in TM regeneration by influencing 17 gene proteins.

FGF2 and EGF for the Regeneration of Tympanic Membrane: A Systematic Review

Objective

A systematic review was conducted to compare the effectiveness and safety of fibroblast growth factor-2 (FGF2) and epidermal growth factor (EGF) for regeneration of the tympanic membrane (TM).

Methods

The PubMed database was searched for relevant studies. Experimental and clinical studies reporting acute and chronic TM perforations in relation to two healing outcomes (success rate and closure time) and complications were selected.

Results

A total of 47 studies were included. Five experimental studies showed closure rates of 55%-100% with FGF2 compared with 10%-62.5% in controls for acute perforations. Five experimental studies showed closure rates of 30.3%-100% with EGF and 3.6%-41% in controls for chronic perforations. Two experimental studies showed closure rates of 31.6% or 85.7% with FGF2 and 15.8% or 100% with EGF. Nine clinical studies of acute large perforations showed closure rates of 91.4%-100% with FGF2 or EGF. Two clinical studies showed similar closure rates between groups treated with FGF2 and EGF. Seven clinical studies showed closure rates of 88.9%-100% within 3 months and 58%-66% within 12 months using FGF2 in repair of chronic perforations, but only one study showed a significantly higher closure rate in the saline group compared with the FGF2 group (71.4% vs. 57.5%, respectively, P = 0.547). In addition, three experimental studies showed no ototoxicity associated with FGF2 or EGF. No middle ear cholesteatoma or epithelial pearls were reported, except in one experimental study and one clinical study, respectively.

Conclusions

FGF2 and EGF showed good effects and reliable safety for the regeneration of TM. In addition, EGF was better for the regeneration of acute perforations, while FGF2 combined with biological scaffolds was superior to EGF for chronic perforations, but was associated with high rates of reperforation over time. Further studies are required to determine whether EGF or FGF2 is better for TM regeneration.

Tympanic membrane regeneration using platelet-rich fibrin: a systematic review and meta-analysis

PURPOSE

Platelet-rich fibrin (PRF) results in satisfactory wound healing. This analysis focuses on assessing the effectiveness of PRF in the treatment of tympanic membrane (TM) perforations.

MATERIALS AND METHODS

The literature was searched using PubMed, Embase, Cochrane Library and Web of Science databases from inception to February 28th, 2021. The following healing and hearing outcomes were measured: closure rate, pre-and postoperative auditory results, and incidence of postoperative infections. Data were pooled and expressed as the odds ratio (OR).

RESULTS

Ten studies were eligible for qualitative review, and seven of them were included for the final quantitative comparison. The OR for the closure rate of acute perforations was 4.30 (95% CI 1.35-13.70, I² = 0%), and the OR in the chronic subgroup was 5.42 (95% CI 2.57-11.43, I² = 0%). The total OR value for the completed closure rate was 5.10 (95% CI 2.72-9.54, I² = 0%), indicating that the utilization of PRF can enhance the closure of both acute and chronic perforations. The qualitative review did not find improved hearing results with the use of PRF. In addition to promoting closure, PRF can reduce the incidence of infections (OR = 0.14). The sensitivity analysis did not change the final results, and there was no publication bias in this analysis.

CONCLUSION

PRF can increase the closure rate of acute perforations, enhance the survival rate of autografts in TM surgeries and reduce the incidence of infections. However, the literature indicates that PRF does not influence the hearing outcomes. This study shows that PRF is an effective agent for TM regeneration.

Butterfly Cartilage Tympanoplasty as an Alternative to Conventional Surgery for Tympanic Membrane Perforations: A Systematic Review and Meta-Analysis

OBJECTIVE

To compare the effectiveness of butterfly cartilage tympanoplasty (BCT) with that of conventional surgical approaches in the treatment of tympanic membrane perforations.

METHODS

A systematic search was performed by screening the PubMed, Embase, and Cochrane Library databases up to October 31, 2020. Two coauthors independently identified studies in accordance with the selection criteria. Data were pooled and analyzed via Review Manager version 5.3 and Stata version 12.0 software. The postoperative outcomes were measured and expressed as odds ratios (ORs) and standardized mean differences (SMDs). Additionally, heterogeneity was assessed through the I² statistic.

RESULTS

A total of 15 articles were eligible for final inclusion. The OR values for the graft uptake rate, compared to conventional tympanoplasty, were 1.12 (95%CI: 0.56-2.22, I² = 52%, P = .75) and 1.22 (95%CI: 0.58-2.59, I² = 0%, P = .60), and the OR compared to fat plug myringoplasty was 3.02 (95%CI: 1.04-8.77, I² = 0%, P = .04). The qualitative analysis of the hearing results reflected significant postoperative auditory gains with no significant differences between the BCT and control groups, indicating satisfactory and similar postoperative hearing improvement. Moreover, the operation time was shortened (SMD = -2.19, 95%CI: -2.79 to -1.59, I² = 82%, P < .05), and the postoperative pain was less with the BCT approach.

CONCLUSION

Butterfly cartilage tympanoplasty has satisfactory efficacy in terms of anatomical and functional results in small to medium perforations. It reduces operation time and postoperative pain. However, the effectiveness on large perforation requires further assessment by well-designed studies.

The Effectiveness of bFGF in the Treatment of Tympanic Membrane Perforations: A Systematic Review and Meta-Analysis

Objective:

To investigate the effectiveness of basic fibroblast growth factor (bFGF) versus placebo or no intervention in the treatment of tympanic membrane (TM) perforations from randomized controlled trials (RCTs), prospective and retrospective studies.

Data Sources:

PubMed, EMBASE, and Cochrane databases were screened from their inceptions to June 2019.

Study Selection:

Inclusion criteria: 1) English language; 2) observational (retrospective or prospective) or treatment (RCT) studies; 3) reported the outcomes on the application of bFGF in adult or pediatric population. Exclusion criteria: 1) studies without a control group; 2) animal studies, in vitro studies, review studies, and case reports.

Data Extraction:

Number of patients, cause of TM perforation, perforation size, treatment, mean age, follow-up time, sex, closure rate, healing time, mean air-bone gap improvement.

Data Synthesis:

A total of 14 studies were included, including seven RCTs and seven non-RCTs with a total of 1,072 participants. The odds ratio for closure rate of bFGF treatment was 7.33 (95% confidence interval [CI], 4.65 to 11.53; p < 0.01; I² = 44%) and the standardized mean difference (SMD) for healing time was –5.89 (95% CI: –7.85 to –3.93, p < 0.01, I² = 98%), suggesting bFGF application has a significant effect on closure of TM perforations. However, no significant change in hearing (SMD: 0.08, 95% CI: –0.11 to 0.27, p = 0.39, I² = 0%) was seen as a result of bFGF treatment.

Conclusions:

Our meta-analysis has revealed that the application of bFGF can significantly enhance the closure rate as well as shorten the healing time for TM perforations. In terms of hearing, there is as yet no evidence that bFGF has a significant effect. Given its ease, availability, and safety, bFGF can be used effectively for TM repair.

Necessities, opportunities, and challenges for tympanic membrane perforation scaffolding-based bioengineering

Tympanic membrane (TM) perforation is a global clinical dilemma. It occurs as a consequence of object penetration, blast trauma, barotrauma, and middle ear diseases. TM perforation may lead to otitis media, retraction pockets, cholesteatoma, and conductive deafness. Molecular therapies may not be suitable to treat perforation because there is no underlying tissue matrix to support epithelium bridging. Chronic perforations are usually reconstructed with autologous grafts via surgical myringoplasty. Surgical treatment is uncomfortable for the patients. The grafting materials are not perfect because they produce an opaque membrane, fail in up to 20% of cases, and are suboptimal to restore acoustic function. Millions of patients from developing parts of the world have not got access to surgical grafting due to operational complexities, lack of surgical resources, and high cost. These shortcomings emphasize bioengineering to improve placement options, healing rate, hearing outcomes, and minimize surgical procedures. This review highlights cellular, structural, pathophysiological, and perforation specific determinants that affect healing, acoustic and surgical outcomes; and integrates necessities relevant to bioengineered scaffolds. This study further summarizes scaffolding components, progress in scaffolding strategies and design, and engenders limitations and challenges for optimal bioengineering of chronic perforation.

Can Tissue Engineering Bring Hope to the Development of Human Tympanic Membrane?

The tympanic membrane (TM), more commonly known as the eardrum, consists of a thin layer of tissue in the human ear that receives sound vibrations from outside of the body and transmits them to the auditory ossicles. The TM perforations (TMPs) are a common ontological condition, which in some cases can result in permanent hearing loss. Despite the spontaneous healing capacity of the TM to regenerate in the majority of cases of acute perforation, chronic perforations require surgical interventions. However, the disadvantages of the surgical procedure include infection, anesthetic risks, and high failure of graft patency. The tissue engineering strategy, which includes the applications of a three-dimensional (3D) scaffold, cells, and biomolecules or a combination of them for the closure of chronic perforation, has been considered as an emerging treatment. Using this approach, emerging products are currently under development to regenerate the TM structure and its properties. This research aimed to highlight the problems with the current methods of TMP treatment, and critically evaluate the tissue engineering approaches, which may overcome these drawbacks. The focus of this review is on recent literature to critically discuss the emerging advanced materials used as a 3D scaffold in the development of a TM with cellular engineering, biomolecules, cells, and the fabrications of the TM and its pathway to the clinical application. In this review, we discuss the properties of TM and the advantages and disadvantages of the current clinical products for repair and replacement of the TM. Furthermore, we provide an overview of the in vitro and preclinical studies of emerging products over the past 5 years. The results of recent preclinical studies suggest that the tissue engineering field holds significant promise.

Silk Fibroin as a Functional Biomaterial for Tissue Engineering

Tissue engineering (TE) is the approach to combine cells with scaffold materials and appropriate growth factors to regenerate or replace damaged or degenerated tissue or organs. The scaffold material as a template for tissue formation plays the most important role in TE. Among scaffold materials, silk fibroin (SF), a natural protein with outstanding mechanical properties, biodegradability, biocompatibility, and bioresorbability has attracted significant attention for TE applications. SF is commonly dissolved into an aqueous solution and can be easily reconstructed into different material formats, including films, mats, hydrogels, and sponges via various fabrication techniques. These include spin coating, electrospinning, freeze drying, physical, and chemical crosslinking techniques. Furthermore, to facilitate fabrication of more complex SF-based scaffolds with high precision techniques including micro-patterning and bio-printing have recently been explored. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have been recently developed. The typical TE applications of SF-based scaffolds including bone, cartilage, ligament, tendon, skin, wound healing, and tympanic membrane, will be highlighted and discussed, followed by future prospects and challenges needing to be addressed.

Acellular Collagen Scaffold With Basic Fibroblast Growth Factor for Repair of Traumatic Tympanic Membrane Perforation in a Rat Model

OBJECTIVE

To evaluate the efficacy of acellular collagen scaffold (ACS) in combination with basic fibroblast growth factor (bFGF) for the repair of traumatic tympanic membrane (TM) perforation in a rat model.

STUDY DESIGN

A prospective controlled animal study in a rat model of traumatic TM perforation.

SETTING

Tertiary medical center.

SUBJECTS AND METHODS

Sprague-Dawley rats (N = 84) with unilateral traumatic perforation of the right TMs were randomized to receive ACS, bFGF, ACS in combination with bFGF (ACS/bFGF), or nothing (spontaneous healing without any interventions as a control group). The healing outcomes were evaluated by otoscopy, optical coherence tomography, histology, and transmission electron microscopy at 1, 2, and 4 weeks postoperatively. The hearing outcomes were assessed with auditory brainstem response testing.

RESULTS

ACS/bFGF resulted in higher perforation closure rates at an earlier stage than spontaneous healing, ACS, and bFGF. Based on histology, optical coherence tomography, and transmission electron microscopy, a trilaminar structure and uniform thickness with mature, densely packed collagen fibers were seen in the ACS/bFGF group. Auditory brainstem response evaluation also showed that ACS/bFGF treatment promoted faster functional hearing recovery as compared with the control group.

CONCLUSIONS

ACS is an effective TM scaffold and a carrier for bFGF. ACS/bFGF improves the TM closure rate, results in better-reconstructed TMs, and improves hearing. ACS/bFGF serves as a potential substitute for TM perforations in clinical settings.

Comparative efficacy of platelet-rich plasma applied in myringoplasty: A systematic review and meta-analysis

BACKGROUND

Tympanic membrane (TM) perforation is quite common in the clinical setting. Chronic TM perforations require surgical treatments such as myringoplasty. Currently, platelet-rich plasma (PRP) is a novel, effective substance that is increasingly utilized for TM perforation repair. This study aims to evaluate the effectiveness of PRP in the application of TM perforation repair.

METHODS

A systematic search was conducted to screen the Medline, Embase, Cochrane, Scopus and Web of Science databases up to July 2020. Studies were identified in accordance with the selection criteria by two coauthors independently. Data regarding the healing and hearing outcomes were pooled and analyzed via Review Manager version 5.3 and STATA version 12.0 software. Odds ratio (OR) was utilized to compare the closure rate. Furthermore, the results of hearing improvements and incidence of complications were also compared to evaluate the effectiveness of PRP.

RESULTS

A total of eight studies with 455 participants were eligible according to the selection criteria. Compared to conventional surgery, the OR of closure was 2.70 (95% CI: 1.27 to 5.76, P = 0.01, I2 = 0%) in randomized controlled trial (RCT) subgroup and 6.18 (95% CI: 2.22 to 17.25, P = 0.0005, I2 = 0) in non-RCT subgroup. The overall OR of closure was 3.69 (95% CI: 2.02 to 6.74, P<0.0001, I2 = 0%), suggesting a significant effect on the healing of TM perforation. Between preoperative and postoperative hearing results, there is no statistical difference between the PRP and the control groups. Additionally, the use of PRP resulted in a lower incidence of complication than the use of conventional approaches.

CONCLUSION

The application of PRP during the TM surgeries can enhance the closure rate, provide similar hearing improvements and decrease the incidence of postoperative complications. Given these advantages, PRP can be considered an effective treatment for TM regeneration.

State of the art regeneration of the tympanic membrane

PURPOSE OF REVIEW

One of the most common diseases of the tympanic membrane is a perforation, and tympanoplasty is one of the more common procedures in otolaryngology. Tympanic membrane regeneration and bioengineering aim to improve the success rate of the procedure, increase the availability of different scaffolds and provide innovative tools that will simplify the surgical technique and make it accessible for surgeons with varying expertise level. This review aims to raise awareness of current tissue engineering developments in tympanic membrane regeneration and how they may augment current clinical practices. We focus here on achievements in tympanic membrane cell cultures and on innovations in development of new scaffolds and growth factors that enhance regeneration of patient's native tympanic membranes.

RECENT FINDINGS

In recent years, great achievements were reached in the field of tympanic membrane regeneration in the three hallmarks of bioengineering: cells, scaffolds and bioactive molecules. New techniques for modeling normal tympanic membrane proliferation were developed, as well as for isolation and expansion of normal tympanic membrane keratinocytes from miniature samples of scarred tissue. Ongoing clinical trials aim to seal the perforation by applying different scaffolds infiltrated by growth factors on the tympanic membrane.

SUMMARY

Research efforts in tympanic membrane regeneration continue to seek the ideal single tissue-engineered substitute. Recent advances in tympanic membrane bioengineering include new types of scaffolds that may augment and provide a safe and effective alternative to the current gold-standard autograft. New bioactive molecules may simplify the surgical procedure and reduce surgical time by augmenting the native tympanic membrane regeneration. Several groups of bioengineering scientists and neurotologists are continuing to move forward and develop new strategies, seeking to create a fully functional tissue-engineered tympanic membrane.

Epidermal Growth Factor-Releasing Radially Aligned Electrospun Nanofibrous Patches for the Regeneration of Chronic Tympanic Membrane Perforations

Chronic tympanic membrane (TM) perforations can cause otorrhea. To date, various types of tissue engineering techniques have been applied for the regeneration of chronic TM perforations. However, the application of nanofibers with radially aligned nanostructures and the simultaneous release of growth factors have never been applied in the regeneration of chronic TM perforations. Here, epidermal growth factor (EGF)-releasing radially aligned nanofibrous patches (ERA-NFPs) are developed and applied for the regeneration of chronic perforated TMs. First, radial alignments and the presence of EGF in the ERA-NFPs are analyzed. EGF is confirmed to be released from the ERA-NFPs until 8 weeks. In an in vitro study, cell viability assay, immunocytochemistry, and wound-healing assay indicate rational enhancement of healing by the combination of radial alignments and EGF release. The effect of ERA-NFPs on TM cells is revealed by quantitative real-time polymerase chain reaction. An in vivo animal study shows that the ERA-NFPs effectively stimulates the healing of the chronic TM perforations. The TMs healed by ERA-NFPs show histological properties similar to those of normal TMs. These results indicate that ERA-NFPs may be an efficient platform for the regeneration of chronic TM perforations, laying the foundation for nonsurgical treatments of chronic otitis media.

Effects of solid acellular type-I/III collagen biomaterials on in vitro and in vivo chondrogenesis of mesenchymal stem cells

INTRODUCTION

Type-I/III collagen membranes are advocated for clinical use in articular cartilage repair as being able of inducing chondrogenesis, a technique termed autologous matrix-induced chondrogenesis (AMIC). Area covered: The current in vitro and translational in vivo evidence for chondrogenic effects of solid acellular type-I/III collagen biomaterials. Expert commentary: In vitro, mesenchymal stem cells (MSCs) adhere to the fibers of the type-I/III collagen membrane. No in vitro study provides evidence that a type-I/III collagen matrix alone may induce chondrogenesis. Few in vitro studies compare the effects of type-I and type-II collagen scaffolds on chondrogenesis. Recent investigations suggest better chondrogenesis with type-II collagen scaffolds. A systematic review of the translational in vivo data identified one long-term study showing that covering of cartilage defects treated by microfracture with a type-I/III collagen membrane significantly enhanced the repair tissue volume compared with microfracture alone. Other in vivo evidence is lacking to suggest either improved histological structure or biomechanical function of the repair tissue. Taken together, there is a paucity of in vitro and preclinical in vivo evidence supporting the concept that solid acellular type-I/III collagen scaffolds may be superior to classical approaches to induce in vitro or in vivo chondrogenesis of MSCs.

Comparative acoustic performance and mechanical properties of silk membranes for the repair of chronic tympanic membrane perforations

The acoustic and mechanical properties of silk membranes of different thicknesses were tested to determine their suitability as a repair material for tympanic membrane perforations. Membranes of different thickness (10-100μm) were tested to determine their frequency response and their resistance to pressure loads in a simulated ear canal model. Their mechanical rigidity to pressure loads was confirmed by tensile testing. These membranes were tested alongside animal cartilage, currently the strongest available myringoplasty graft as well as paper, which is commonly used for simpler procedures. Silk membranes showed resonant frequencies within the human hearing range and a higher vibrational amplitude than cartilage, suggesting that silk may offer good acoustic energy transfer characteristics. Silk membranes were also highly resistant to simulated pressure changes in the middle ear, suggesting they can resist retraction, a common cause of graft failure resulting from chronic negative pressures in the middle ear. Part of this strength can be explained by the substantially higher modulus of silk films compared with cartilage. This allows for the production of films that are much thinner than cartilage, with superior acoustic properties, but that still provide the same level of mechanical support as thicker cartilage. Together, these in vitro results suggest that silk membranes may provide good hearing outcomes while offering similar levels of mechanical support to the reconstructed middle ear.

A prospective cohort study of the silk fibroin patch in chronic tympanic membrane perforation

OBJECTIVES/HYPOTHESIS

Silk fibroin patching has been used to repair acute tympanic membrane perforations. Here, we describe the advantages and outcomes of this technique for chronic tympanic membrane perforations.

STUDY DESIGN

Individual cohort study.

METHODS

Forty patients were enrolled; half underwent perichondrium myringoplasty, and the silk fibroin patch technique was applied in the remaining patients. We compared the closure, otorrhea, and complication rates; closure time; postoperative hearing gain; and patient satisfaction between the two groups.

RESULTS

Demographic data (gender, site, age, duration, preoperative air-bone gap, and perforation size and location) were not significantly different between the two groups. The closure rates and times, complication rates, and postoperative hearing gains were also similar in both groups. The mean operative time, otorrhea rate, and complication rate were also significantly better in the silk fibroin patch group. The intraoperative dizziness scores were higher in the conventional perichondrium myringoplasty group.

CONCLUSIONS

Success rates were similar for the silk fibroin patch technique and conventional perichondrium myringoplasty; however, patching was an easier, faster procedure. Our results suggest that the silk fibroin patch technique is a suitable treatment for chronic tympanic membrane perforation.

LEVEL OF EVIDENCE

2b Laryngoscope, 126:2798-2803, 2016.

Topical application of epidermal growth factor with no scaffold material on the healing of human traumatic tympanic membrane perforations

OBJECTIVE

We evaluated the effects of conservative treatment and topical application of epidermal growth factor (EGF) with no scaffold material on the healing of human traumatic tympanic membrane perforations (TMPs).

STUDY DESIGN

Prospective, randomised clinical trial.

METHODS

A prospective analysis was performed between January 2015 and March 2015 for the treatment of human traumatic TMPs. The closure rate, closure time, hearing gain and rate of purulent otorrhoea were compared between the topical application of EGF and conservative treatment.

RESULT

In total, 97 patients were analysed. The total closure rates did not significantly differ between the observation and EGF groups (83.0% versus 92.0%, P = 0.182). The total average closure time in the observation group was significantly longer than in the EGF group (25.1 ± 10.5 versus 11.7 ± 5.2 days, P = 0.001). When the closure rate was evaluated according to perforation size, no significant difference was seen for medium or large perforations (P = 0.18 and 0.21, respectively). When closure time was evaluated according to perforation size, a significant difference was seen for medium and large perforations (P = 0.001).

CONCLUSIONS

This study suggests that topical application of EGF with no scaffold material may significantly shorten the closure time of human traumatic TMPs. Such a shorter recovery time may lead to reduced healthcare costs. This alternative technique to a classic myringoplasty is particularly beneficial and suitable for the closure of large human traumatic TMPs.

Application of Collagen Scaffold in Tissue Engineering: Recent Advances and New Perspectives

Collagen is the main structural protein of most hard and soft tissues in animals and the human body, which plays an important role in maintaining the biological and structural integrity of the extracellular matrix (ECM) and provides physical support to tissues. Collagen can be extracted and purified from a variety of sources and offers low immunogenicity, a porous structure, good permeability, biocompatibility and biodegradability. Collagen scaffolds have been widely used in tissue engineering due to these excellent properties. However, the poor mechanical property of collagen scaffolds limits their applications to some extent. To overcome this shortcoming, collagen scaffolds can be cross-linked by chemical or physical methods or modified with natural/synthetic polymers or inorganic materials. Biochemical factors can also be introduced to the scaffold to further improve its biological activity. This review will summarize the structure and biological characteristics of collagen and introduce the preparation methods and modification strategies of collagen scaffolds. The typical application of a collagen scaffold in tissue engineering (including nerve, bone, cartilage, tendon, ligament, blood vessel and skin) will be further provided. The prospects and challenges about their future research and application will also be pointed out.

Rat model of chronic tympanic membrane perforation: Ventilation tube with mitomycin C and dexamethasone

OBJECTIVE

Chronic tympanic membrane perforation (TMP) in a clinical setting may attract surgical intervention. With the advent of modern biomaterials, new options are available for myringoplasty but safety and efficacy need evaluation in a chronic TMP animal model. The aim of this study was to evaluate the efficacy of ventilation tube (VT) insertion in conjunction with topical application of mitomycin C/dexamethasone (M/D) for the creation of chronic TMP in rats.

METHODS

Thirty male Sprague-Dawley rats underwent myringotomy of the right tympanic membrane (TM) and were divided into three experimental groups: spontaneous healing (myringotomy control), VT insertion for 2 weeks and VT insertion for 2 weeks in conjunction with topical application of M/D (VT-M/D). All TMs were regularly assessed by otoscopy for 10 weeks and then animals were sacrificed for histological evaluation.

RESULTS

In the VT-M/D group, seven out of ten (70%) perforations were patent at 10 weeks (mean patency, 57.9 days; P<0.01). The VT group had two out of ten (20%) perforations patent at 10 weeks (mean patency, 26.5 days; P<0.01), while all TMPs from the myringotomy control group were closed by day 9 (mean patency, 7.2 days). Histologically, the TMPs patent at week 10 had a stratified squamous epithelialized rim, keratinocyte layer thickening around the perforation edge as well as increased collagen deposition and macrophage infiltration.

CONCLUSION

Chronic TMP in a rat model was successfully created by VT insertion and the efficacy was increased in combination with topical application of M/D.

Searching for a rat model of chronic tympanic membrane perforation: Healing delayed by mitomycin C/dexamethasone but not paper implantation or iterative myringotomy

OBJECTIVES

Surgical intervention such as myringoplasty or tympanoplasty is an option in the current clinical management of chronic tympanic membrane perforation (TMP). Animal models of chronic TMP are needed for pre-clinical testing of new materials and to improve existing techniques. We evaluated several reported animal model techniques from the literature for the creation of chronic TMPs. The aim of this study was to evaluate production of chronic TMPs in a rat model using topical mitomycin C/dexamethasone, paper insertion into middle ear cavity (MEC) or re-myringotomy.

METHODS

Forty male Sprague-Dawley rats underwent myringotomy of the right tympanic membrane (TM) and were randomly divided into 3 experimental groups: application of topical mitomycin C/dexamethasone, paper insertion into middle ear cavity, or re-myringotomy. Control perforations were allowed to close spontaneously. TMs were assessed regularly with otoscopy for 8 weeks. At the end of 8 weeks, animals were sacrificed for histology.

RESULTS

The closure of TMPs was significantly delayed by mitomycin C/dexamethasone (mean patency, 18.9 days; P≤0.01) compared with the control (mean patency, 7 days), but was not significantly delayed in the paper insertion group (mean patency, 9.4 days; P=0.74). Repeated myringotomy of closed perforations (mean number of myringotomies, 8.9 per ear) stimulated acceleration of closure rather than delay. Histologically, the mitomycin C/dexamethasone group had almost normal TM morphology, while the paper insertion group revealed inflammatory and granulomatous responses. The re-myringotomy group had a thickened TM fibrous layer with collagen deposition.

CONCLUSIONS

Mitomycin C/dexamethasone delayed TMP closure in rats but the effect was not sufficiently long-lasting to be defined as a chronic TMP. Neither paper insertion into middle ear cavity nor re-myringotomy created chronic TMP in rats.

Clinical outcomes of silk patch in acute tympanic membrane perforation

Objectives

The silk patch is a thin transparent patch that is produced from silk fibroin. In this study, we investigated the treatment effects of the silk patch in patients with traumatic tympanic membrane perforation (TTMP).

Methods

The closure rate, otorrhea rate, and closure time in all patients and the closure time in successful patients were compared between the paper patch and silk patch groups.

Results

Demographic data (gender, site, age, traumatic duration, preoperative air-bone gap, and perforation size and location) were not significantly different between the two groups. The closure rate and otorrhea rate were not significantly different between the two groups. However, the closure time was different between the two groups (closure time of all patients, P=0.031; closure time of successful patients, P=0.037).

Conclusion

The silk patch which has transparent, elastic, adhesive, and hyper-keratinizing properties results in a more efficient closure time than the paper patch in the treatment of TTMP patients. We therefore believe that the silk patch should be recommended for the treatment of acute tympanic membrane perforation.

Outlook for Tissue Engineering of the Tympanic Membrane

Tympanic membrane perforation is a common problem leading to hearing loss. Despite the autoregenerative activity of the eardrum, chronic perforations require surgery using different materials, from autologous tissue - fascia, cartilage, fat or perichondrium - to paper patch. However, both, surgical procedures (myringoplasty or tympanoplasty) and the materials employed, have a number of limitations. Therefore, the advances in this field are incorporating the principles of tissue engineering, which includes the use of scaffolds, biomolecules and cells. This discipline allows the development of new biocompatible materials that reproduce the structure and mechanical properties of the native tympanic membrane, while it seeks to implement new therapeutic approaches that can be performed in an outpatient setting. Moreover, the creation of an artificial tympanic membrane commercially available would reduce the duration of the surgery and costs. The present review analyzes the current treatment of tympanic perforations and examines the techniques of tissue engineering, either to develop bioartificial constructs, or for tympanic regeneration by using different scaffold materials, bioactive molecules and cells. Finally, it considers the aspects regarding the design of scaffolds, release of biomolecules and use of cells that must be taken into account in the tissue engineering of the eardrum. The possibility of developing new biomaterials, as well as constructs commercially available, makes tissue engineering a discipline with great potential, capable of overcoming the drawbacks of current surgical procedures.

Animal models of chronic tympanic membrane perforation: a 'time-out' to review evidence and standardize design

OBJECTIVE

To review the literature on techniques for creation of chronic tympanic membrane perforations (TMP) in animal models. Establishing such models in a laboratory setting will have value if they replicate many of the properties of the human clinical condition and can thus be used for investigation of novel grafting materials or other interventions.

METHODS

A literature search of the PubMed database (1950-August 2014) was performed. The search included all English-language literature published attempts on chronic or delayed TMP in animal models. Studies of non English-language or acute TMP were excluded.

RESULTS

Thirty-seven studies were identified. Various methods to create TMP in animals have been used including infolding technique, thermal injury, re-myringotomy, and topical agents including chemicals and growth factor receptor inhibitors. The most common type of animal utilized was chinchilla, followed by rat and guinea pig. Twenty three of the 37 studies reported success in achieving chronic TMP animal model while 14 studies solely delayed the healing of TMP. Numerous experimental limitations were identified including TMP patency duration of <8 weeks, lack of documentation of total number of animals attempted and absence of proof for chronicity with otoscopic and histologic evidence.

CONCLUSION

The existing literature demonstrates the need for an ideal chronic TMP animal model to allow the development of new treatments and evaluate the risk of their clinical application. Various identified techniques seem promising, however, a need was identified for standardization of experimental design and evidence to address multiple limitations.

Animal models of chronic tympanic membrane perforation: in response to plasminogen initiates and potentiates the healing of acute and chronic tympanic membrane perforations in mice

Tympanic membrane perforations (TMP) are relatively common but are typically not treated in their acute stage, as most will heal spontaneously in 7–10 days. Those cases which fail to heal within 3 months are called chronic TMP which attract surgical intervention (e.g. myringoplasty), typically with a temporalis fascia autograft. New materials for the repair of chronic TMP are being developed to address deficiencies in the performance of autografts by undergoing evaluation in animal models prior to clinical study. However, there is currently a lack of ideal chronic TMP animal models available, hindering the development of new treatments. Various techniques and animal species have been investigated for the creation of chronic TMP with varied success. In the present commentary, we bring to the attention of readers the recent report by Shen et al. in Journal of Translational Medicine. The study reported the creation of a chronic TMP animal model in plasminogen gene deficient mice. However, the short observation time (9, 19 days), lack of success rate and the scarcity of solid evidence (e.g. otoscopic & histologic images) to confirm the chronicity of TMP warrant a more thorough discussion.

The biocompatibility of silk fibroin and acellular collagen scaffolds for tissue engineering in the ear

Recent experimental studies have shown the suitability of silk fibroin scaffold (SFS) and porcine-derived acellular collagen I/III scaffold (ACS) as onlay graft materials for tympanic membrane perforation repair. The aims of this study were to further characterize and evaluate the in vivo biocompatibility of SFS and ACS compared with commonly used materials such as Gelfoam and paper in a rat model. The scaffolds were implanted in subcutaneous (SC) tissue and middle ear (ME) cavity followed by histological and otoscopic evaluation for up to 26 weeks. Our results revealed that SFS and ACS were well tolerated and compatible in rat SC and ME tissues throughout the study. The tissue response adjacent to the implants evaluated by histology and otoscopy showed SFS and ACS to have a milder tissue response with minimal inflammation compared to that of paper. Gelfoam gave similar results to SFS and ACS after SC implantation, but it was found to be associated with pronounced fibrosis and osteoneogenesis after ME implantation. It is concluded that SFS and ACS both were biocompatible and could serve as potential alternative scaffolds for tissue engineering in the ear.

Plasminogen initiates and potentiates the healing of acute and chronic tympanic membrane perforations in mice

BACKGROUND

Most tympanic membrane (TM) perforations heal spontaneously, but approximately 10-20% remain open as chronic TM perforations. Chronic perforations can lead to an impaired hearing ability and recurrent middle ear infections. Traditionally, these perforations must be surgically closed, which is costly and time consuming. Therefore, there is a need for simpler therapeutic strategies. Previous studies by us have shown that plasminogen (plg) is a potent pro-inflammatory regulator that accelerates cutaneous wound healing in mice. We have also shown that the healing of TM perforations is completely arrested in plg-deficient (plg(-/-)) mice and that these mice develop chronic TM perforations. In the present study, we investigated the therapeutic potential of local plg injection in acute and chronic TM perforation mice models.

METHODS

Plg(-/-) mice and wild-type mice were subjected to standardized TM perforations followed by local injection of plg into the soft tissue surrounding the TM. TM perforations with chronic characteristics were induced by leaving TM perforations in plg(-/-) mice untreated for 9 days before treatment. The healing process was observed through otomicroscope and finally confirmed by immunostaining. The quality of TM healing was evaluated based on the morphology of the TM.

RESULT

Daily local injections of plg into the soft tissue surrounding the TM restored the ability to heal TM perforations in plg-/- mice in a dose-dependent manner, and potentiated the healing rate and quality in wild-type mice. A single local injection of plg initiated the healing of the chronic-like TM perforations in these mice, resulting in a closed TM with a continuous but rather thick outer keratinocyte layer. However, three plg injections led to a completely healed TM with a thin keratinizing squamous epithelium covering a connective tissue layer.

CONCLUSION

Our data suggests that plg is a promising drug candidate for the treatment of chronic TM perforations in humans.